getting integer from a string

[zhar999]

how do i extract the string to an integer? ask the user to input fraction but in a form of a string, and i want to get the numerator and denominator in int type so as to perform arithmetic to another fraction.

for example, 13/27

how do i get the 13 as a numerator and 27 as a denominator?

[nano511]

... What is the point of asking for it as a string? Wouldn't it be much easier to ask for them as ints?

[shacktar]

Given a string, you can convert it to an int using a stringstream.

#include <string>
#include <sstream>
using namespace std;

int main()
{
     string intAsString = "42";
     int asInt = 0;

     stringstream ss;
     ss<<intAsString;
     ss>>asInt; //convert string into int and store it in "asInt"
     ss.str(""); //clear the stringstream
     ss.clear(); //clear error flags because "42" is not a valid stream (?)

     //here asInt == 42

     return 0;
}

If the user enters a fraction like you say above, you could use getline with '/' as the delimiter to extract the numerator, and getline again to extract the denominator.

#include <string>
#include <iostream>
using namespace std;

int main()
{
     string numerator, denominator;

     cout<<"Enter fraction in the form 'int/int'"<<endl;

     getline(cin, numerator, '/'); //read up to the '/' and store it in numerator. Discard the '/'
     getline(cin, denominator); //read up to the newline and store it in denominator. Discard the '\n'

     //if the user entered 47/1236, then
     //numerator == "47"
     //denominator == "1236"

     //use a stringstream here to convert to ints!

     return 0;
}

[zhar999]

@nano, it's our assigment and it said that the user must enter a string, i wish it's integer :(

[zhar999]

@shackstar, can you explain to me the sstream im not familiar with it, thanks! :)

[zhar999]

why do i need to initialize the

string intAsString = "42";
     int asInt = 0;

[shacktar]

You don't need to initialize it as "42". That was just an example. You could pass it in numerator as a string (and convert it to an int as in the first example), and then pass it in denominator as a string (and convert it to an int).

Here is a reference for the stringstream object:
http://www.cplusplus.com/reference/iostream/stringstream/

can you explain to me the sstream im not familiar with it

Do you know how when you do cin>> and expect an int (or some other data type), it converts the user input to that data type?

float aFloat;
int anInt;

cout<<"Type in a float"<<endl;
cin>>aFloat;
cin.ignore(1000, '\n'); //remove newline from the stream

cout<<"Now type in an integer"<<endl;
cin>>anInt;
cin.ignore(1000, '\n'); //remove newline from the stream 

stringstreams allow you to use that functionality but without the stream being tied into standard in, or a file stream, etc. Essentially, you pass in the stream as a string to the stringstream using the << operator, and then the stringstream object allows you to play with the stream as if it were cin or an ifstream, for example. When you're done with using a particular string as the stream, remember to clear the stringstream using the call .str("") (see the first example).

[zhar999]

there's something wrong with this one, when i check if i really did convert the string to int by using arithmetic to the converted strings the denominator seems not working, it remain as zero

string num1;
	string den1;
	string num2;
	string den2;
	int n1=0;
	int d1=0;

case 1:{
            cout<<"Addition"<<endl;
            getline(cin,num1,'/');
            getline(cin,den1);  //<-maybe there's a problem in getting the den?
			getline(cin,num2,'/');
			getline(cin,den2);

			stringstream ss;
			ss<<num1;
			ss>>n1;
			ss.str("");
			ss<<den1;
			ss>>d1; 
			ss.str("");
			cout<<n1+1<<"/"<<d1<<endl; //<-the output of d1 is zero even the input is 5 for example
            break;
			   }

[shacktar]

Apparently, you have to call ss.clear(); after ss.str("");. That's strange because that has worked for me in the past. ss.clear(); clears the error flags, so maybe just passing it a string without an end of file character causes the stringstream to be in a bad state? I will change my examples above.

[zhar999]

case 1:{
            cout<<"Addition"<<endl;
            getline(cin,num1,'/');
            getline(cin,den1);
			getline(cin,num2,'/');
			getline(cin,den2);

			stringstream ss;
			ss<<num1;
			ss>>n1;
			ss.str("");
			ss.clear();
			ss<<den1;
			ss>>n1;
			ss.str("");
			ss.clear();
			cout<<n1<<"/"<<d1<<endl;
            break;
			   }

still doesn't work

[shacktar]

It worked for me after I changed the second ss>>n1; to ss>>d1; ;)

[zhar999]

oh yes! it worked! maybe it's a sign that i must go and eat, anyways, thanks a lot! *thumbsup